114 research outputs found
Nonorthogonal Multiple Access in Large-Scale Underlay Cognitive Radio Networks
In this paper, non-orthogonal multiple access (NOMA) is applied to
large-scale underlay cognitive radio (CR) networks with randomly deployed
users. In order to characterize the performance of the considered network, new
closed-form expressions of the outage probability are derived using
stochastic-geometry. More importantly, by carrying out the diversity analysis,
new insights are obtained under the two scenarios with different power
constraints: 1) fixed transmit power of the primary transmitters (PTs), and 2)
transmit power of the PTs being proportional to that of the secondary base
station. For the first scenario, a diversity order of is experienced at the
-th ordered NOMA user. For the second scenario, there is an asymptotic error
floor for the outage probability. Simulation results are provided to verify the
accuracy of the derived results. A pivotal conclusion is reached that by
carefully designing target data rates and power allocation coefficients of
users, NOMA can outperform conventional orthogonal multiple access in underlay
CR networks.Comment: Accepted by IEEE Transactions on Vehicular Technolog
Fairness of User Clustering in MIMO Non-Orthogonal Multiple Access Systems
In this letter, a downlink multiple-input-multiple-output non-orthogonal multiple access scenario is considered. We investigate a dynamic user clustering problem from a fairness perspective. In order to solve this optimization problem, three sub-optimal algorithms, namely, top-down A, top-down B, and bottom up, are proposed to realize the different tradeoffs of complexity and throughput of the worst user. In addition, for each given user clustering case, we optimize the power allocation coefficients for the users in each cluster by adopting a bisection search-based algorithm. Numerical results show that the proposed algorithms can lower the complexity with an acceptable degradation on the throughput compared with the exhaustive search method. It is worth noting that the top-down B algorithm can achieve a good tradeoff between the complexity and the throughput among the three proposed algorithms
Variance-Constrained Capacity of the Molecular Timing Channel with Synchronization Error
Accepted for GLOBECOM 201
Optimization of Grant-Free NOMA With Multiple Configured-Grants for mURLLC
15 pages, 15 figures, submitted to IEEE JSAC SI on Next Generation Multiple Access. arXiv admin note: text overlap with arXiv:2101.0051515 pages, 15 figures, submitted to IEEE JSAC SI on Next Generation Multiple Access. arXiv admin note: text overlap with arXiv:2101.0051
Active RIS Versus Passive RIS: Which Is Superior with the Same Power Budget?
This letter theoretically compares the active reconfigurable intelligent surface (RIS)-aided system with the passive RIS-aided system. For a fair comparison, we consider that these two systems have the same overall power budget that can be used at both the base station (BS) and the RIS. For active RIS, we first derive the optimal power splitting between the BS’s transmit signal power and RIS’s output signal power. We also analyze the impact of various system parameters on the optimal power splitting ratio. Then, we theoretically and numerically compare the performance between the active RIS and the passive RIS, which demonstrates that the active RIS would be superior if the power budget is not very small and the number of RIS elements is not very large
Beamforming based Mitigation of Hovering Inaccuracy in UAV-Aided RFET
Hovering inaccuracy of unmanned aerial vehicle (UAV) degrades the performance of UAV-aided radio frequency energy transfer (RFET). Such inaccuracy arises due to positioning error and rotational motion of UAV, which lead to localization mismatch (LM) and orientation mismatch (OM). In this paper, antenna array beam steering based UAV hovering inaccuracy mitigation strategy is presented. The antenna beam does not accurately point towards the field sensor node due to rotational motion of the UAV along with pitch, roll, and yaw, which leads to deviation in the elevation angle. An analytical framework is developed to model this deviation, and its variation is estimated using the data collected through an experimental setup. Closed-form expressions of received power at the field node are obtained for the four cases arising from LM and OM. An optimization problem to estimate the optimal system parameters (transmit power, UAV hovering altitude, and antenna steering parameter) is formulated. The problem is proven to be nonconvex. Therefore, an algorithm is proposed to solve this problem. Simulation results demonstrate that the proposed framework significantly mitigates the hovering inaccuracy; compared to reported state-of-the-art the same performance can be achieved with substantially less transmit power
A Survey of Downlink Non-orthogonal Multiple Access for 5G Wireless Communication Networks
Accepted by ZTE CommunicationsAccepted by ZTE CommunicationsAccepted by ZTE CommunicationsAccepted by ZTE CommunicationsAccepted by ZTE CommunicationsNon-orthogonal multiple access (NOMA) has been recognized as a promising multiple access technique for the next generation cellular communication networks. In this paper, we first discuss a simple NOMA model with two users served by a single-carrier simultaneously to illustrate its basic principles. Then, a more general model with multicarrier serving an arbitrary number of users on each subcarrier is also discussed. An overview of existing works on performance analysis, resource allocation, and multiple-input multiple-output NOMA are summarized and discussed. Furthermore, we discuss the key features of NOMA and its potential research challenges
Cooperative Non-orthogonal Multiple Access With Simultaneous Wireless Information and Power Transfer
Accepted by IEEE Journal on Selected Areas in Communications (JSAC
Secrecy and Energy Efficiency in Massive MIMO Aided Heterogeneous C-RAN: A New Look at Interference
In this paper, we investigate the potential benefits of the massive
multiple-input multiple-output (MIMO) enabled heterogeneous cloud radio access
network (C-RAN) in terms of the secrecy and energy efficiency (EE). In this
network, both remote radio heads (RRHs) and massive MIMO macrocell base
stations (BSs) are deployed and soft fractional frequency reuse (S-FFR) is
adopted to mitigate the inter-tier interference. We first examine the physical
layer security by deriving the area ergodic secrecy rate and secrecy outage
probability. Our results reveal that the use of massive MIMO and C-RAN can
greatly improve the secrecy performance. For C-RAN, a large number of RRHs
achieves high area ergodic secrecy rate and low secrecy outage probability, due
to its powerful interference management. We find that for massive MIMO aided
macrocells, having more antennas and serving more users improves secrecy
performance. Then we derive the EE of the heterogeneous C-RAN, illustrating
that increasing the number of RRHs significantly enhances the network EE.
Furthermore, it is indicated that allocating more radio resources to the RRHs
can linearly increase the EE of RRH tier and improve the network EE without
affecting the EE of the macrocells.Comment: 26 pages, 11 figures, to appear in IEEE Journal of Selected Topics in
Signal Processin
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